简单工厂（不属于GOF23）

简介

只需要传入响应的参数就可以获取所需要的对象而无需知道其细节
工厂类的职责相对过重，增加新产品需要修改工厂类的判断逻辑
违背开闭原则

工厂类创建的对象比较少的情况下可已使用简单工厂

Coding

package com.yulang.design_pattern_23.simpleFactory;
public class VideoFactory {
    public Video build(String type){
        if("java".equals(type)){
            return new JavaVideo();
        }else if ("python".equals(type)){
            return new PythonVideo();
        }else{
            throw  new  UnsupportedOperationException();
        }
    }
}

package com.yulang.design_pattern_23.simpleFactory;
public abstract class Video {
    public abstract void produce();
}

package com.yulang.design_pattern_23.simpleFactory;
public class JavaVideo extends Video {
    @Override
    public void produce() {
        System.out.println("java");
    }
}

package com.yulang.design_pattern_23.simpleFactory;
public class PythonVideo extends Video {
    @Override
    public void produce() {
        System.out.println("python");
    }
}

package com.yulang.design_pattern_23.simpleFactory;
public class Test {
    public static void main(String[] args) {
        VideoFactory videoFactory = new VideoFactory();
        videoFactory.build("java33").produce();
    }
}

利用反射实现

package com.yulang.design_pattern_23.simpleFactory;
public class VideoFactory {
    public Video build(Class c){
        Video video = null;
        try {
            video = (Video) Class.forName(c.getName()).newInstance();
        } catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) {
            e.printStackTrace();
        }
        return video;
    }
}

package com.yulang.design_pattern_23.simpleFactory;
public class Test {
    public static void main(String[] args) {
        VideoFactory videoFactory = new VideoFactory();
        videoFactory.build(JavaVideo.class).produce();
    }
}

JDK源码

Calendar 类中的

    private static Calendar createCalendar(TimeZone zone,
                                           Locale aLocale)
    {
        CalendarProvider provider =
            LocaleProviderAdapter.getAdapter(CalendarProvider.class, aLocale)
                                 .getCalendarProvider();
        if (provider != null) {
            try {
                return provider.getInstance(zone, aLocale);
            } catch (IllegalArgumentException iae) {
                // fall back to the default instantiation
            }
        }
        Calendar cal = null;
        if (aLocale.hasExtensions()) {
            String caltype = aLocale.getUnicodeLocaleType("ca");
            if (caltype != null) {
                switch (caltype) {
                case "buddhist":
                cal = new BuddhistCalendar(zone, aLocale);
                    break;
                case "japanese":
                    cal = new JapaneseImperialCalendar(zone, aLocale);
                    break;
                case "gregory":
                    cal = new GregorianCalendar(zone, aLocale);
                    break;
                }
            }
        }
        if (cal == null) {
            // If no known calendar type is explicitly specified,
            // perform the traditional way to create a Calendar:
            // create a BuddhistCalendar for th_TH locale,
            // a JapaneseImperialCalendar for ja_JP_JP locale, or
            // a GregorianCalendar for any other locales.
            // NOTE: The language, country and variant strings are interned.
            if (aLocale.getLanguage() == "th" && aLocale.getCountry() == "TH") {
                cal = new BuddhistCalendar(zone, aLocale);
            } else if (aLocale.getVariant() == "JP" && aLocale.getLanguage() == "ja"
                       && aLocale.getCountry() == "JP") {
                cal = new JapaneseImperialCalendar(zone, aLocale);
            } else {
                cal = new GregorianCalendar(zone, aLocale);
            }
        }
        return cal;
    }

**